We have isolated and characterized a new LTR-retrotransposon in the genome of the Mediterranean fruit fly (Medfly), Ceratitis capitata. This retrotransposon, which we named yoyo, appears to be a member of the gypsy/Ty3 class of elements. The yoyo element was originally discovered on the Y chromosome of the Medfly. Although the Y chromosome copy appears to be truncated, at least two other apparently complete copies of yoyo from other genomic locations have been isolated and characterized. The complete element is approximately 7.7 kb in size. In addition to fairly typical GAG and POL coding regions, the yoyo element contains a potential ENV gene. The presence of an ENV gene is a key feature distinguishing potential retroviral-like elements, such as gypsy (and possibly yoyo), from many other invertebrate retrotransposons previously described. In addition to the structural features of yoyo, evidence is provided to show that yoyo is capable of movement in the genome, including RFLPs showing variability in genomic localization of copies of yoyo between strains, and differences among individuals in the presence of yoyo at a specific site in the genome.